The present invention relates to a roughing and finishing end mill.
There is known a roughing end mill which makes highly efficient rough working possible by cutting chips into small pieces by blades provided with notches.
Recently, with the widespread use of a machining center, NC (numerically controlled) machine tool or the variety of requirements of users, the demand for a roughing and finishing end mill which is highly efficient and which does not require that finishing work be performed on the milled workpiece is increasing.
These have been well known for use as roughing end mills the so-called backing-off end mills the flanks of the circumferential edges of the blades of which are off-center in a cross-sectional view through the axis of the end mill as shown in FIG. 1(a) and the conventional type end mill with flat circumferential edge blades shown in FIG. 1(b). In these figures, the broken line indicates the shape of the bottom surface of a notch formed in the circumferential surface or the backing off for cutting chips into pieces.
The present invention relates to the shape and the arrangement of notches provided in each blade to form cutting parts which are defined between the notches in the blades of the roughing end mill of the type shown in FIG. 1(b).
In the conventional end mill, the notches are formed in either of two ways. One is to provide notches 3 on the plural helical blades 2 perpendicularly to the axis of rotation as shown in FIG. 2(b), and the other way is to cause the notches to extend helically to extend helically (left-hand helix in most cases) to the axis of rotation as shown in FIG. 2(b).
In the arrangement shown in FIG. 2(a), the blades and notches are arranged so that there will be no portions of the workpiece left without being worked on by the mill, that is, so that during one revolution of the tool it performs cutting work on the workpiece without leaving any portion unworked. Therefore, a notch in a neighbouring blade is shifted toward the end of the blade or toward the shank of the tool relative to any given notch. However, in the case of cutting with a tool, in which the notches are perpendicular to the blade body, the side-clearance angle of the main body is zero. In this case, a heavy wear of the corner is caused, and a special machine tool for exclusive use on such cutting is necessary and the working time may become longer.
In the latter (the case shown in FIG. 2(b)), the cutting in a single screw thread causes the blade to be offset as much as amount of the lead of the screw, making always the negative side of the side clearance the main blade, so that cutting is unfavorably done by the side not suitable for cutting. Therefore it has been suggested that the angle of the blades be changed by employment of multiple screw threads for cutting by the positive side of the side clearance angle, and the arrangement of notches in neighbouring helical blades be shifted in the reverse direction (Public Notice of patent application in Japan, 1975, No. 50-31312).
However, according to the working as described above, the number of blades for receiving notches determines the shape of the blades and the side clearance angle. Also, this arrangement may have following faults: be selected. The notch does not play a role in the function of the blade when it is shallow after it is reworked because the bottom of notch is on a circumference. The frequency of reworking of the blade is decreased.